I wouldn't get rid of the snails you already have. Just get rid of the plants you have, they are most likely the problem. As ILoveMyAbbyGirl said, they will keep the walls of your tank clean. Plus their fun to watch How big are the snales and how big are the Gold fish? We put several small snales in our tank and the Goldfish just ate them. Hopefully you manage to stop the snail infestation :P